Presently, as a red light emitting semiconductor device (red semiconductor light emitting device, or semiconductor device, light emitting diode, LED), widely used is a semiconductor device having an AlGaInP layer provided as a light emitting layer on a GaAs substrate.
However, since this red light emitting semiconductor device contains harmful elements such as As and P, environmentally-friendly red light emitting semiconductor devices not containing these harmful elements are eagerly desired because of recent enhancement of environmental awareness.
For this reason, there are investigations for manufacturing a red light emitting semiconductor device using a nitride semiconductor, which is known as a semiconductor material for a blue light emitting semiconductor device.
As an example thereof, there is an investigation of obtaining a red light emitting semiconductor device using a semiconductor obtained by adding high concentration In to GaN. However, when the In content becomes higher, the piezoelectric field effect ascribable to strain of a crystal becomes more remarkable and the luminous efficiency as a red light emitting semiconductor device becomes lower. Thus, such a technology is not realized under the present conditions.
Under such a state, paying attention to wide gap of a nitride semiconductor, use of a semiconductor obtained by adding (doping) Eu to a base material GaN as a red light emitting semiconductor device material is investigated and attracting attention (Patent Document 3, Non-patent Documents 1-5). However, the resultant semiconductor has poor crystal quality. Further, high voltage of tens to hundreds of V is necessary for light emission. Thus, it is problematic to adopt such a semiconductor as a red light emitting semiconductor device material.
Further, there is also an investigation of fabricating a fluorescent substance layer obtained by adding Eu to a GaInN-based semiconductor and causing red light emission from this fluorescent substance layer. However, there is a problem that luminous efficiency is not sufficient since it is an indirect light emission mechanism in which red light emission is caused by excitation of the fluorescent substance layer by blue light emission (Patent Documents 1, 2, 4, 5).